Domain-wall topology induced by spontaneous symmetry breaking in polariton graphene

TL;DR

This paper investigates how spontaneous symmetry breaking in polariton graphene leads to domain formation with topologically protected chiral currents, revealing a novel interplay between valley topology and condensate dynamics.

Contribution

It demonstrates the emergence of valley-polarized domains and topologically protected chiral currents due to symmetry breaking in polariton condensates on a graphene lattice.

Findings

Valley-polarized domains form following the Kibble-Zurek scenario.

Walls between domains host topologically protected chiral currents.

Symmetry breaking selects a single valley, breaking time-reversal symmetry.

Abstract

We present a numerical study of exciton-polariton (polariton) condensation in a staggered polariton graphene showing a gapped s-band at the $K$ and $K'$ valleys. The condensation occurs at $K$ or $K'$, at the kinetically-favorable negative mass extrema of the valence band. Considering attractive polariton-polariton interaction allows to generate a spatially extended condensate. Spontaneous symmetry breaking occurring during the condensate build-up leads to the formation of valley-polarized domains following the Kibble-Zurek scenario. The selection of a single valley breaks time-reversal symmetry and the walls separating domains exhibit a topologically-protected chiral current. This current therefore emerges as a result of the interplay between the non-trivial valley topology and the condensation-induced symmetry breaking.